// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef UI_GFX_SELECTION_MODEL_H_
#define UI_GFX_SELECTION_MODEL_H_

#include <stddef.h>

#include <string>

#include "ui/gfx/gfx_export.h"
#include "ui/gfx/range/range.h"

namespace gfx {

// VisualCursorDirection and LogicalCursorDirection represent directions of
// motion of the cursor in BiDi text. The combinations that make sense are:
//
//  base::i18n::TextDirection  VisualCursorDirection  LogicalCursorDirection
//       LEFT_TO_RIGHT             CURSOR_LEFT           CURSOR_BACKWARD
//       LEFT_TO_RIGHT             CURSOR_RIGHT          CURSOR_FORWARD
//       RIGHT_TO_LEFT             CURSOR_RIGHT          CURSOR_BACKWARD
//       RIGHT_TO_LEFT             CURSOR_LEFT           CURSOR_FORWARD
enum VisualCursorDirection {
    CURSOR_LEFT,
    CURSOR_RIGHT
};
enum LogicalCursorDirection {
    CURSOR_BACKWARD,
    CURSOR_FORWARD
};

// TODO(xji): publish bidi-editing guide line and replace the place holder.
// SelectionModel is used to represent the logical selection and visual
// position of cursor.
//
// For bi-directional text, the mapping between visual position and logical
// position is not one-to-one. For example, logical text "abcDEF" where capital
// letters stand for Hebrew, the visual display is "abcFED". According to the
// bidi editing guide (http://bidi-editing-guideline):
// 1. If pointing to the right half of the cell of a LTR character, the current
// position must be set after this character and the caret must be displayed
// after this character.
// 2. If pointing to the right half of the cell of a RTL character, the current
// position must be set before this character and the caret must be displayed
// before this character.
//
// Pointing to the right half of 'c' and pointing to the right half of 'D' both
// set the logical cursor position to 3. But the cursor displayed visually at
// different places:
// Pointing to the right half of 'c' displays the cursor right of 'c' as
// "abc|FED".
// Pointing to the right half of 'D' displays the cursor right of 'D' as
// "abcFED|".
// So, besides the logical selection start point and end point, we need extra
// information to specify to which character the visual cursor is bound. This
// is given by a "caret affinity" which is either CURSOR_BACKWARD (indicating
// the trailing half of the 'c' in this case) or CURSOR_FORWARD (indicating
// the leading half of the 'D').
class GFX_EXPORT SelectionModel {
public:
    // Create a default SelectionModel to be overwritten later.
    SelectionModel();
    // Create a SelectionModel representing a caret |position| without a
    // selection. The |affinity| is meaningful only when the caret is positioned
    // between bidi runs that are not visually contiguous: in that case, it
    // indicates the run to which the caret is attached for display purposes.
    SelectionModel(size_t position, LogicalCursorDirection affinity);
    // Create a SelectionModel representing a selection (which may be empty).
    // The caret position is the end of the range.
    SelectionModel(const Range& selection, LogicalCursorDirection affinity);

    const Range& selection() const { return selection_; }
    size_t caret_pos() const { return selection_.end(); }
    LogicalCursorDirection caret_affinity() const { return caret_affinity_; }

    // WARNING: Generally the selection start should not be changed without
    // considering the effect on the caret affinity.
    void set_selection_start(uint32_t pos) { selection_.set_start(pos); }

    bool operator==(const SelectionModel& sel) const;
    bool operator!=(const SelectionModel& sel) const { return !(*this == sel); }

    std::string ToString() const;

private:
    // Logical selection. The logical caret position is the end of the selection.
    Range selection_;

    // The logical direction from the caret position (selection_.end()) to the
    // character it is attached to for display purposes. This matters only when
    // the surrounding characters are not visually contiguous, which happens only
    // in bidi text (and only at bidi run boundaries). The text is treated as
    // though it was surrounded on both sides by runs in the dominant text
    // direction. For example, supposing the dominant direction is LTR and the
    // logical text is "abcDEF", where DEF is right-to-left text, the visual
    // cursor will display as follows:
    //    caret position    CURSOR_BACKWARD affinity    CURSOR_FORWARD affinity
    //          0                  |abcFED                     |abcFED
    //          1                  a|bcFED                     a|bcFED
    //          2                  ab|cFED                     ab|cFED
    //          3                  abc|FED                     abcFED|
    //          4                  abcFE|D                     abcFE|D
    //          5                  abcF|ED                     abcF|ED
    //          6                  abc|FED                     abcFED|
    LogicalCursorDirection caret_affinity_;
};

} // namespace gfx

#endif // UI_GFX_SELECTION_MODEL_H_
